Stop! Atoms

An "atomic coilgun" that can stop atoms in their tracks using a sequence of pulsed magnetic fields has been developed by US scientists. The device opens up the possibility of slowing and trapping atoms regardless of atomic number, which is not possible with laser trapping that works only for certain atoms.

In 1997, the Nobel Prize for Physics was awarded to three scientists for their combined contributions to laser cooling, a method used to cool gases and bring their usually high-speed antics to a standstill. However, while these "atom traps" have proved very useful to physical scientists, laser cooling unfortunately excludes important elements, such as hydrogen, iron, nickel and cobalt, which cannot undergo a closed two-level transition. As such, a method of trapping atoms has been sought that works with all elements including the archetypal atom - hydrogen.

Now, Mark Raizen and his colleagues at The University of Texas at Austin, have taken an important step in the control of atoms that can bring their speeds down from thousands of kilometres per hour, to just a few kilometres per hour to trap them. They realised that while not all elements can undergo the appropriate transition to be cooled by a laser, almost all elements, and many molecules are paramagnetic and so can be affected by a magnetic field.

The researchers, inspired by the coilgun devised by scientists in the University's Center for Electromechanics, have now developed an "atomic coilgun" that slows and gradually stops atoms with a sequence of pulsed magnetic fields.

"Of particular importance are the doors being opened for our understanding of hydrogen", says Raizen, precision spectroscopy of hydrogen's isotopes, deuterium and tritium, continues to be of great interest to both atomic and nuclear physics. Further study of tritium, as the simplest radioactive element, also serves as an ideal system for the study of beta decay."

The prototype atomic coilgun is built around an 18-coil device that can stop a supersonic beam of metastable neon atoms. The team is now developing a 64-stage device that could be used to slow hydrogen atoms.